Such container floor plates are, for example, known from WO 88/07485 A1. In this document the upper floor layer is described to be formed by several panels arranged next to each other in parallel to the longitudinal direction of the container, the panels having a number of T-shaped projections also extending in parallel to the longitudinal direction and pointing upwards. The upper surfaces of these T-shaped projections form the “floor” of the container. Between the projections channels remain, through which the cooling air can be guided.
Support blocks made of foam with high density are located between the upper floor layer and the lower floor layer. These support blocks serve as distance pieces during manufacturing of the floor plate. The distance pieces are placed on the lower floor layer. The upper floor layer is placed on the distance pieces. This construction is then placed in a hydraulic press. The hollow space remaining between the upper floor layer and the lower floor layer is then filled with foam that has, in the solid state, approximately the same density as the support blocks. On its lower side, the lower floor layer forms open tunnels, into which the tines of a fork lift can be inserted.
For many years, containers have been used for transporting goods all over the world. Containers have the advantage that they can be transported on both ships, railway wagons and trucks, so that a shift between different transport systems can be made without requiring the unloading of the goods transported in containers.
In many cases, the outer measurements of such containers are standardised. A typical container has a cuboid or box shape, meaning that it has two end walls, two side walls, a roof plate and a floor plate. Usually a door arrangement is located in at least one end wall. The entire container is mechanically stiffened by a frame structure, so that several containers can be stacked. At each end wall the frame structure has a support frame, the support frames being connected to each other by means of two or four longitudinal beams.
Two longitudinal beams extend along the lower edge of the two side walls. The floor plate is connected to the longitudinal beams, the force transmission being realisable in different manners. Typically, a container must be able to stand relatively large point loads of up to 7.5 t. Fittings for fixing the container on ships, trucks, railway wagons, or for fixing the containers to each other, are located at the corners of the container.
The first containers had floor plates, where boards or beams were supported on transversal metal supports having a C-shaped cross-section. The ends of the transversal supports were welded onto the longitudinal supports. This construction was also used in the first generation of refrigerated containers, the wooden floor plates eventually being replaced by a sandwich-construction of a so-called T-floor, an insulating layer and a lower floor layer. The T-floor has several T-shaped profiles arranged next to each other, whose upper surfaces form the floor of the container that is visible from above, channels for cooling air being formed between the T-profiles.
In principle such a construction is known from DE 94 19 348 U1. The lower floor layer is formed by a wave-like profile, in which, compared to a regular wave profile, some waves have been left out. The upper floor layer is supported by the lower floor layer via the insulating layer. The consequence of this is that the insulating layer also has to carry the weight of the goods transported in the container and accordingly has to be rather solid. This again results in reduced insulating properties.
WO 95/15289 A1 shows a different refrigerated container, in which an insulating foam layer is also arranged between the upper floor layer and the lower floor layer. Also here the insulating layer must be able to carry the entire load.
U.S. Pat. No. 5,979,684 shows a freight container, in which the floor plate and other components are made of a fibre-reinforced plastic material, the fibre-reinforced plastic material surrounding a core of plastic foam. For the support of the upper layer of the fibre-reinforced plastic material by the lower layer of fibre-reinforced plastic material, I-shaped, C-shaped and Z-shaped profiles made of a fibre-reinforced plastic material are provided. In the direction of the load, however, these profiles have a relatively poor rigidity, so that also here the core originally foreseen for insulation purposes must have a sufficient load-carrying capacity. The demands on the carrying properties and the demands on the insulation properties contrast with each other.
In the known constructions, the sandwich of upper floor layer, insulating layer and lower floor layer is susceptible to delamination. If the bonding between the layers fails, the rigidity and the strength of the floor are substantially impaired. This can, for example, be caused by ingressing humidity and is a frequent reason for repair work on known containers.